No-vent liquid hydrogen storage and delivery system

ABSTRACT

A hydrogen storage and delivery system is provided having an orifice pulse tube refrigerator and a liquid hydrogen storage vessel. A cooling system, coupled to the orifice pulse tube refrigerator, cools the vessel and abates ambient heat transfer thereto in order to maintain the liquid hydrogen in the vessel at or below its saturation temperature. Hydrogen boil-off, and the necessity to provide continuous venting of vaporized hydrogen are minimized or avoided. In a preferred embodiment, the hydrogen storage vessel has a toroidal shape, and the pulse tube refrigerator is a two stage pulse tube refrigerator and extends within a central void space defined at the geometric center of the toroidal storage vessel. Also in a preferred embodiment, the cooling system includes first and second thermal jackets, each having a substantially toroidal shape and enclosing the storage vessel, wherein each of the thermal jackets is thermally coupled to one of the first or second stages of the pulse tube refrigerator in order to cool the vessel and to abate ambient heat leak thereto. The hydrogen storage and delivery system is particularly suitable for use in vehicles, such as passenger automobiles.

This application is a continuation of co-pending U.S. patent applicationSer. No. 10/820,654, which claims the benefit of U.S. Provisional PatentApplication Ser. No. 60/461,639 filed Apr. 9, 2003, the contents ofwhich are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a system for storing and dispensingliquid hydrogen without venting, and more particularly to such a storageand delivery system for use in an automobile, light or heavy dutytrucks, boats, or transportation systems or vehicles in general that usehydrogen for fuel, such that a vehicle can store a large quantity ofhydrogen fuel in the liquid state without requiring hydrogen venting dueto boil-off.

2. Description of Related Art

Recently, and especially in view of the global oil climate, theautomotive industry has reported serious development efforts to producehydrogen powered vehicles. A key benefit to using hydrogen as opposed toconventional fossil fuels is that hydrogen burns cleanly, producing onlywater as a combustion product, it yields no carbon monoxide or carbondioxide emissions, and it dramatically reduces NO_(x) emissions. Whenused with fuel cells, hydrogen reacts with oxygen and produces onlywater. Furthermore, hydrogen fuel is abundantly available in limitlesssupply, whereas existing fossil fuel reserves are finite, and eventuallywill run out. For these reasons, hydrogen would seem to be an ideal fuelfor modern automobiles. However, widespread use of hydrogen asautomobile fuel has been prevented due to several major concerns.

In particular, storing and handling liquid hydrogen is difficult and canbe dangerous. Hydrogen is highly combustible and is prone to explodewhen combined with atmospheric oxygen in the presence of an ignitionsource. In addition, hydrogen has a very high vapor pressure, boiling atabout 20K under atmospheric pressure. Therefore, conventionally hydrogenis stored either in its gaseous state in high pressure tanks (about oreven greater than 5000 psia gaseous hydrogen), or in low pressure liquidstorage vessels which must be vented to relieve hydrogen overpressure asa result of vaporization due to ambient heat leak into the storagevessels (e.g. typical ambient temperature of about 298K or 25° C.).

Neither of these hydrogen storage mechanisms is suitable for use inprivately owned and operated automobiles. First, at 5000 psia,conventional size high-pressure storage tanks can hold only a relativelysmall amount of hydrogen, i.e. about 2-4 kg. The size of these tanks isfurther limited due to space and weight constraints in an automobile.The limited storage volume for hydrogen fuel means limited automobiledriving range between refuelings. Another perhaps more significantdisadvantage is that storing a highly explosive fuel, such as gaseoushydrogen, at high pressure on the order of 5000 psia in an automobilepresents a significant danger to both occupants and bystanders shouldthe pressure tank or associated high pressure hardware fail.

Second, conventional low pressure liquid hydrogen storage vessels areunsuitable for storing hydrogen fuel in automobiles due to therequirement of venting vaporized hydrogen gas to the atmosphere.Hydrogen overpressure results from heat transfer from the environmentinto the storage vessel causing liquid hydrogen to boil and vaporize.The hydrogen vapor continues to expand as ambient heat energy is furtherabsorbed, and the storage tanks must be vented of this hydrogen vapor toprevent explosion of the vessel due to hydrogen overpressure. Therefore,today's typical liquid hydrogen storage systems involve or requirecontrolled venting of boil-off hydrogen gas whose release into theatmosphere must be directed and controlled to prevent concentratedpockets hydrogen gas in confined spaces (e.g. inside buildings) where itmay explode or cause a fire. For these reasons, existing hydrogen ventstypically are located in remote areas or at safe distances above thetallest structure in the vicinity of the vent. If the quantity of ventedhydrogen is sufficiently large then burn-off stacks usually must beutilized.

It is easy to understand why it will be impractical for every parkingspace, garage, and driveway to be equipped with a hydrogen vent stackfor venting hydrogen overpressure while a hydrogen-powered vehicle isparked. In fact, even if it were possible to provide such stationaryhydrogen vent stacks, automobiles are by definition “mobile,” and it istotally impractical to limit people to stationing their cars only inlocations where there is an available hydrogen vent stack. In addition,the near continuous venting of hydrogen gas is a significant waste offuel that greatly diminishes the efficiency of a hydrogen-poweredautomobile.

Several automotive manufacturers have conducted experiments involvingvehicles that operate using hydrogen in both liquid and gaseous forms,however no one has yet devised a mechanism for storing highly denseliquid hydrogen (compared to gaseous hydrogen) in a hydrogen-poweredautomobile which does not require venting to relieve hydrogenoverpressure.

Another technology that has been proposed to store large quantities ofhydrogen is surface-adsorption onto a metal-hydride matrix. It has beenreported that hydrogen densities (mass hydrogen per storage volume)comparable to liquid hydrogen can be obtained via this technique ofadsorbing onto the surface of metal hydride matrices, however theinventors have not been able to verify this. Regardless, there are stillseveral disadvantages to the use of metal hydrides for storing gaseoushydrogen. First, storing hydrogen in this manner requires ultra highpurity hydrogen gas; even very small amounts of common contaminants suchas carbon monoxide would significantly decrease the metal hydrideadsorptive storage capacity for hydrogen. Second, to date only verysmall metal hydride containers (e.g. for use in portable electronicdevices) have been developed, and it is not clear that extrapolatingthis concept to the scale required to store a reasonable quantity ofhydrogen fuel for an automobile would be straight-forward or evenpossible. Third, the exotic metals required to produce metal hydridematrices for hydrogen storage would be cost prohibitive on the scalerequired to provide adequate hydrogen storage capacity for anautomobile. Fourth, metal hydride hydrogen adsorption systems are veryheavy, and may contribute significantly to the weight of an automobile.

Accordingly, there is a need in the art for a system for storinghydrogen fuel in liquid form in a hydrogen-powered automobile or in anautomobile equipped with a hydrogen powered fuel cell, that does notneed to be vented to relieve hydrogen overpressure.

SUMMARY OF THE INVENTION

A hydrogen storage and delivery system is provided, having a liquidhydrogen storage vessel, a substantially vertically oriented orificepulse tube refrigerator, and a cooling system coupled to the orificepulse tube refrigerator. The cooling system is adapted to counteract orabate heat transfer to the storage vessel from the ambient environment.

An automobile having a hydrogen-powered internal combustion engineand/or a hydrogen powered fuel cell, and a hydrogen storage and deliverysystem also is provided, wherein the system includes a liquid hydrogenstorage vessel, an orifice pulse tube refrigerator, and a cooling systemcoupled to the orifice pulse tube refrigerator. The cooling system isadapted to counteract or abate heat transfer to the storage vessel fromthe ambient environment.

A hydrogen storage and delivery system also is provided having atoroidal liquid hydrogen storage vessel, an orifice pulse tuberefrigerator, and a cooling system. The toroidal storage vessel has aninterior surface defining a liquid hydrogen storage volume, and thestorage vessel further defines a void space located at the geometriccenter of the storage vessel. The orifice pulse tube refrigeratorextends within the void space at the geometric center of the storagevessel. The orifice pulse tube refrigerator includes a first stage pulsetube refrigeration unit and a second stage pulse tube refrigerationunit, each of the first and second stage refrigeration units having arespective regenerator, cold heat exchanger, pulse tube and hot heatexchanger, wherein net refrigeration power for each of the first andsecond stage refrigeration units is generated at the respective firstand second stage cold heat exchangers. The cooling system includes afirst thermal jacket in the shape of a toroid located concentricallyadjacent and substantially enclosing the liquid hydrogen storage vessel,and a second thermal jacket in the shape of a toroid locatedconcentrically adjacent and substantially enclosing the first thermaljacket.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view, partially in cross-section, of a liquidhydrogen storage and delivery system according to a preferred embodimentof the invention, including a toroidal hydrogen storage vessel and atwo-stage orifice pulse tube refrigeration unit.

FIG. 2 is a top isometric view, partially broken away, of the liquidhydrogen storage and delivery system of FIG. 1.

FIG. 3 is a centerline exploded view of the liquid hydrogen storage anddelivery system of FIG. 1.

FIG. 4 is a close-up schematic view of the two-stage orifice pulse tuberefrigeration unit shown in FIG. 1.

FIG. 5 is a schematic view, partially in section, of a liquid hydrogenstorage system according to an alternate embodiment of the invention,including a generally rectilinear hydrogen storage vessel.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

As used herein, when a range such as 5 to 25 (or 5-25) is given, thismeans preferably at least 5, and separately independently, preferablynot more than 25. Unless otherwise specified, all components describedherein are made from conventional materials in a conventional manner.

A liquid hydrogen storage and delivery system 10 is provided that iscooled via an orifice pulse tube refrigerator. In its broadest aspect,the invention includes a liquid hydrogen storage vessel 20, an orificepulse tube refrigerator (OPTR) 30, and a cooling system 40 coupled tothe OPTR 30 and adapted to cool the storage vessel 20, or to shield itfrom ambient thermal energy. In the preferred embodiment, the OPTR 30has two cooling or refrigeration stages as more fully described below.The storage and delivery system 10 is suitable to be provided orincorporated into an automobile equipped with a hydrogen poweredinternal combustion engine, and/or a hydrogen powered fuel cell, tostore liquid hydrogen without the need for venting. As used herein, anautomobile can be any ground transportation vehicle, including but notlimited to cars, trucks, trains, etc. It is also believed the systemcould be adapted to store liquid hydrogen in aircraft and watercraft. Avehicle, as used herein, includes automobiles, aircraft and watercraft.

Referring to FIGS. 1-3, a preferred embodiment of the invention isshown. In this embodiment, the hydrogen storage vessel 20 is providedgenerally in the shape of a hollow toroid, whose interior surfacedefines a hydrogen storage volume 25. The toroidal hydrogen storagevessel 20 is substantially enclosed by first and second thermal jackets42 and 44 respectively. The thermal jackets 42 and 44 are positionedconcentrically with respect to the hydrogen storage vessel 20, with thefirst thermal jacket 42 provided adjacent, preferably substantially incontact with the outer surface of the vessel 20, and the second thermaljacket 44 provided adjacent and substantially enclosing the firstthermal jacket 42. In the illustrated embodiment, the first thermaljacket is provided as a length of copper tubing wound around the storagevessel 20, substantially around the entire circumference thereof. Aswill be evident from the figures, the copper tubing of the first thermaljacket 42 is wound or coiled into an overall substantially toroidalshape around and enclosing the toroidal vessel 20. Preferably, thecopper tubing of the first thermal jacket 42 is brazed or soldered tothe outer surface of the vessel 20 in order to promote efficientconductive heat transfer from the vessel wall to the refrigerant fluidthat circulates through the tubing. To facilitate intimatesurface-to-surface contact between the tubing of the jacket 42 and thesurface of the vessel 20, the tubing can be provided having at least oneflat side extending longitudinally along its outer surface; i.e. asD-shaped tubing having a D-shaped cross section, with the flat sideprovided (brazed) against the vessel 20 surface.

A layer of super insulation 60 preferably is disposed over the firstthermal jacket 42, substantially enclosing it and the vessel 20. Thesecond thermal jacket 44 preferably also is provided as a length ofcopper tubing, also wound or coiled so as to define an overallsubstantially toroidal shape around and enclosing the first thermaljacket 42, the vessel 20 and a portion of the super insulation 60.Preferably, the second thermal jacket 44 is spaced a distance from thefirst thermal jacket 42, and is provided or embedded within the superinsulation 60. Preferably, the super insulation 60 comprisesdouble-aluminized Mylar film layers with Dacron netting spacers betweenthe Mylar layers as known in the art. (Mylar and Dacron are registeredtrademarks of DuPont). Preferably, the super insulation 60 has a Mylarlayer density of 52 layers per inch or about 52 layers per inch. Whenthe super insulation 60 is provided as multiple layers of superinsulation material, the second thermal jacket 44 tubing can be providedbetween adjacent layers of the insulation material.

Cooling of the liquid storage vessel 20, and effective shielding of thevessel 20 from ambient heat leak are achieved by circulating arefrigerated fluid or refrigerant through the copper tubing of the firstthermal jacket 42. In addition, the magnitude of ambient heat transferto the first thermal jacket 42 is minimized by circulating a refrigerantthrough the copper tubing of the second thermal jacket 44, therebylowering the required cooling duty of the first thermal jacket 42 tocounteract thermal energy transfer to the vessel 20. The mechanisms forcirculating and refrigerating the refrigerants are described more fullybelow. It should be noted here, however, that each of the thermaljackets has circulated therethrough a separate refrigerant, and eachjacket is maintained at a different temperature, with the first(innermost) jacket 42 being maintained at a lower temperature (describedin detail below). The refrigerants circulated through the first andsecond thermal jackets 42 and 44 can be the same fluid material (i.e.they can both be helium), but they are separately circulated andseparately refrigerated from one another.

In an alternate embodiment, each of the first and second thermal jackets42 and 44 can have an inner wall and an outer wall (relative to thecross-sectional diameter of the respective jacket), defining a generallyannular toroidal jacketing volume for each thermal jacket. In thisalternative embodiment, cooling of the liquid storage vessel 20 isachieved by circulating a refrigerated fluid or refrigerant through thejacketing volumes of each of the thermal jackets 42 and 44. Thisembodiment generally is less preferred due to the potential fornonuniform circulation of the refrigerants through the annular toroidaljacketing volumes.

In a further alternative embodiment, the first and second thermaljackets 42 and 44 can be provided having only a single wall, such thatthe first jacketing volume is defined between the first jacket 42 andthe outer surface of the vessel 20, and the second jacketing volume isdefined between the second jacket 44 and the first jacket 42. Thisembodiment also is less preferred because of the potential fornonuniform circulation of the refrigerants through annular toroidaljacketing volumes.

Most preferably, the liquid storage vessel 20 is provided having aunitary construction, and is not assembled from respective halves viaflanges or mechanical fasteners. However, it is permissible tomanufacture the vessel 20 in halves, and then to weld the halvestogether, e.g., at inner and outer circumferential weld seams, so as toprovide an integrally formed finished vessel 20 of unitary construction.Preferably, the vessel 20 is made from stainless steel, less preferablyfrom aluminum, carbon composite or other composite materials, lesspreferably any other material suitable for storing cryogenic fluids,particularly cryogenic liquid hydrogen at or below 20K, and capable ofwithstanding an internal pressure of at least 40, preferably 50,preferably 60, preferably 80, preferably 100, preferably 200, preferably500, preferably 1000, psia. The liquid hydrogen typically will be storedas a refrigerated liquid not exceeding about 30-50 psia, and thepressure ratings described in the preceding sentence are preferred toprovide a factor of safety.

The liquid level (of hydrogen) in the vessel 20 preferably is measuredusing a flexible temperature and liquid level sensing probe 70 that isarranged generally vertically within the vessel 20. Preferably, thesensing probe 70 extends from at or adjacent the base of the storagevolume 25 of the vessel 20, up to a position at or adjacent the topmostportion or ceiling of the storage volume 25. Preferably, the sensingprobe 70 is one as described in U.S. Pat. No. 6,431,750, the contents ofwhich are incorporated herein by reference. In this embodiment, thesensing probe 70 is made from a number of adhered flexible dielectricstrips with a series of temperature sensing units 71 disposed at spacedintervals along the length of the probe. The probe 70 is flexible atroom temperature, and remains flexible at cryogenic temperatures atleast down to about 60-80K. The temperature sensing units 71 areeffective to measure cryogenic liquid hydrogen temperatures at differentlevels within the storage vessel 20, and can distinguish betweencryogenic liquid hydrogen and cold hydrogen vapor as described in theaforementioned U.S. patent. The preferred sensing probe 70 can beoriented generally into any length-wise shape within the contour of thevessel 20 to measure the temperature gradient of liquid hydrogentherein. Data from the temperature sensing units 71 indicate how fullthe vessel 20 is, and also are used to determine the required coolingduty for the OPTR 30 to maintain the vessel 20 at the desiredtemperature, e.g. at or below 20K (the boiling point of liquidhydrogen). Less preferably, other suitable cryogenic liquid sensingprobes can be used, which generally are known or conventional in theart.

In the illustrated embodiment, the sensing probe 70 is located in arigid housing or sheath 75 that conforms to the desired path of theprobe 70 through the hydrogen storage volume 25. The sheath 75 has aplurality of spaced port holes 76 to permit free flow of hydrogen(liquid or gaseous) to facilitate intimate contact of the hydrogen withthe sensing units 71. The sheath 75 holds the probe 70 in the desiredconformation regardless of the dynamic flow conditions of the liquidhydrogen in the vessel 20. The sheath can be made from stainless steel,or any other suitable material for a cryogenic hydrogen environment.Alternatively, the rigid sheath can be provided having any suitableconstruction; e.g. it can be provided as a recessed groove or slot inthe vessel inner wall, as a series of retainer structures that are fixedwithin the storage volume 25 and adapted to hold the probe 70, etc.

It will be evident from the above description, as well as from FIGS. 1-3(particularly FIGS. 2-3), that the liquid storage vessel 20, the firstthermal jacket 42 and the second thermal jacket 44 are provided asconcentric toroids sharing a common axis of revolution 4, with eachsuccessive toroid having a larger cross-sectional diameter than thetoroid it encloses. Throughout the rest of the specification, theconcentric liquid storage vessel 20, first thermal jacket 42 and secondthermal jacket 44 collectively are referred to as the liquid hydrogenstorage assembly 99.

To assemble the liquid hydrogen storage assembly 99, first the liquidhydrogen storage vessel 20 is provided as described above. Then thecopper tubing of the first thermal jacket 42 is wrapped around the outerwall of the vessel 20 and preferably is brazed or soldered thereto. Thena layer of super insulation 60 is provided over the first thermal jacket42 and the enclosed vessel 20, with the second thermal jacket 44embedded within the thickness (or provided between adjacent layers of)the super insulation 60. Alternatively, when walled thermal jackets areused, these jackets can be assembled from respective first and secondclamshell halves, e.g., joined at seams via suitable or conventionaltechniques, such as vacuum flanges, or other conventional techniquesknown or devisable by persons of ordinary skill in the art.

The liquid hydrogen storage assembly 99 is housed within an outerhousing 50. The housing 50 preferably is generally circular and definesa substantially toroidal passageway 52 at or adjacent its periphery thatis dimensioned to accommodate the hydrogen storage assembly 99 therein.As best seen in FIGS. 1 and 3, the housing 50 preferably includes afirst recessed annular portion 54, a second recessed annular portion 55,and first and second center plates 56 and 57. Alternatively, therecessed annular portions can be provided having the respective centerplates formed integrally therewith or otherwise prefabricated (such asby welding) thereto. By recessed annular portion, it is meant thatportions 54 and 55 each have a generally annular recess or valley suchthat when the portions 54 and 55 are joined together, the respectiverecesses define the toroidal passageway 52 referred to above.

The first and second recessed annular portions 54 and 55 are secured toone another by an interface flange 59. The first and second centerplates 56 and 57 are secured to the respective first and second annularportions 54 and 55 by additional interface flanges 59. Preferably, theflanges 59 are effective to provide a vacuum seal between adjacentportions of the housing 50, such that a primary vacuum chamber 80 isdefined by and within the space enclosed by first and second recessedannular portions 54 and 55, and first and second center plates 56 and57. The primary vacuum chamber 80 preferably is maintained under vacuumat reduced pressure, preferably about or less than 10, 9, 8, 7, 6, 5, 4,3, 2, 1, 0.5, 0.4, 0.3, 0.2, 0.1, 0.05, 0.01, psia, more preferablyabout or less than 10⁻², preferably 10⁻³, preferably 10⁻⁴, preferably10⁻⁵, torr. The primary vacuum chamber 80 acts as a further thermalinsulation jacket surrounding the hydrogen storage assembly 99, and alsothe operative cold components of the OPTR 30 later described, shieldingthese components against heat transfer from the environment. Inaddition, by maintaining the chamber 80 under constant vacuum, leaks ineither of the first or second refrigerant circuits (for first or secondthermal jackets 42 or 44), or in the hydrogen storage vessel can bedetected and monitored by monitoring the pressure in the chamber 80.

The hydrogen storage assembly 99 is suspended or secured within thehousing 50 by a plurality of spacer supports 62 provided between thestorage vessel 20 and the inner surface of at least the second (orbottom) annular portion 55. The supports 62 extend through holes cut orprovided in the super insulation 60, and in between adjacent coppertubing windings of the respective first and second thermal jackets 42and 44. The spacer supports 62 preferably are made from a low thermalconductivity material since they are in physical contact with both theliquid hydrogen storage vessel 20 (which holds liquid hydrogen 5) andthe outer housing 50 (which interfaces the ambient atmosphere).Preferably, the spacer supports 62 are made from G-10 which is a known,conventional fiberglass insulation material suitable for this purpose.Alternatively, the spacer supports 62 can be made from another suitablefiberglass woven epoxy composite material such as Kevlar or S-glass,less preferably another suitable material having a low thermalconductivity.

The components of the housing 50 preferably are made from stainlesssteel, less preferably from lightweight graphite/epoxy material, lesspreferably some other material capable of sustaining a vacuum asdescribed above within the primary vacuum chamber 80.

In addition to the primary vacuum chamber 80, a secondary chamber 90 isprovided, apart from the chamber 80, to house the hydrogen conditioningequipment (vaporizer 92 and preheater 94) which generally is maintainedat a relatively high temperature compared to the storage vessel 20 andthe OPTR 30. The hydrogen conditioning equipment is used to conditionthe hydrogen into a suitable gaseous state (temperature and pressure)prior to being delivered (via delivery valve 96) to the hydrogen fuelintake system of a vehicle. In the illustrated embodiment, the secondarychamber 90 is provided and defined between the second recessed annularportion 55, the second center plate 57, and a third center plate 58 thatis secured to the base of the portion 55 opposite the second centerplate 57. Most preferably, the secondary chamber 90 also is maintainedunder vacuum, preferably 10⁻² to 10⁻⁴ torr or lower, in order to preventor minimize convective heat transfer from the relatively hightemperature components housed therein to walls in common with theprimary vacuum chamber 80. The secondary chamber 90 can be provided withinsulation material, such as glass beads or perlite. When maintainedunder a constant vacuum, the pressure within secondary chamber 90 can bemonitored to detect hydrogen leaks in any of the conditioning equipmentor associated piping.

The hydrogen conditioning equipment preferably includes a vaporizer 92and a preheater 94. In operation, cryogenic liquid hydrogen 5 flowsthrough a delivery pipe 401 equipped with a liquid trap 402 to thevaporizer 92, where the cryogenic liquid is vaporized to provide a coldgas; e.g. 20-100K. On exit from the vaporizer 92, the cold hydrogen gasis delivered into a preheater 94 which further heats the gas to asuitable temperature (e.g. 270-300K) for delivery to a hydrogen-poweredinternal combustion engine (not shown) or to a hydrogen powered fuelcell (also not shown) via delivery valve 96. The vaporizer 92 andpreheater 94 preferably are provided as conventional heat exchangers,suitable or adapted to operate with cryogenic fluids, and can be madefrom conventional materials. In a vehicle, these heat exchangersadvantageously can be supplied with a “hot” fluid such as heated water,coolant or other suitable heated fluid from an associated reservoir orcirculating system for that fluid in the vehicle. The necessary flowrates and temperatures for these “hot” fluids in the vaporizer 92 andpreheater 94 will be determined based on the required heating duty tovaporize and preheat the hydrogen at the necessary flow rate for thegaseous hydrogen fuel, as will be understood by a person having ordinaryskill in the art. Alternatively, the vaporizer 92 and/or preheater 94can be electrically heated.

The delivery valve 96 can be provided as an electronically controlledmetering valve, designed to respond to a throttle demand from the driverof a vehicle. Alternatively, other suitable or conventional controlmechanisms for regulating the flow of hydrogen through the valve 96 canbe used.

The foregoing description and FIGS. 1-3 have been provided based on asubstantially toroidal hydrogen storage vessel 20, whose shape ingeometric terms is a solid of revolution produced by revolving (orintegrating) a circle about a non-intersecting axis, thereby defining acentrally located void space. However, it will be understood that theinvention is not to be correspondingly limited to vessels and associatedthermal jackets having a toroidal shape; other configurations, producedby the revolution of other, non-circular shapes about non-intersectingaxes are possible, and are within the scope of the present invention. Inaddition, the storage vessel 20 can be produced by joining discretesections, e.g. of pipe, to produce a closed hydrogen storage vessel thatdefines a void space at the center to accommodate the OPTR 30. Thetoroidal structure described above is preferred for ease of fabrication,and also for improved physical strength (bursting resistance) over theother configurations described in this paragraph, in part due to theabsence of sharp bends in the vessel wall.

Thus far, the description has focused on the structure and function ofthe housing 50, the liquid hydrogen storage assembly 99 and theconditioning equipment. Though the storage vessel 20 is well shieldedagainst ambient heat transfer via the primary vacuum chamber 80 and thesuper insulation 60, some degree of heat transfer into the vessel 20inevitably will occur. This added thermal energy must be counteracted byremoving an equivalent amount of thermal energy from the vessel 20 inorder to maintain the liquid hydrogen 5 below its saturation temperatureto avoid boil off and hydrogen overpressure. The OPTR 30, mentionedabove, supplies the necessary cooling duty by refrigerating therefrigerant fluids circulating through the first and second thermaljackets 42 and 44, and its structure and operation will now bedescribed.

The OPTR preferably is provided mounted to or through the first centerplate 56 as shown in FIGS. 1 and 3, such that the operative coldcomponents are housed within the primary vacuum chamber 80 while warmercomponents are disposed outside the chamber 80. The OPTR 30 is shown ina close-up schematic, partially sectioned view in FIG. 4. The OPTR 30has a first stage 100 and a second stage 200. Each stage is a separateorifice pulse tube refrigeration unit. Orifice pulse tube refrigerationunits generally are known in the art, and are described for example byC. Wang et al., “A Two-stage Pulse Tube Cooler Operating Below 4K”,Cryogenics, Volume 37, Number 3, 1997, pp. 159-164. In the presentinvention, each stage preferably has a U-tube configuration as shown inFIG. 4; i.e. the working fluid pathways from the first stage regenerator120 to the first stage pulse tube 140, and from the second stageregenerator 220 to the second stage pulse tube 240, are U-shaped. Asevident from FIGS. 1 and 3, the OPTR 30 preferably is orientedvertically in the hydrogen storage and delivery system 10. By verticallyoriented, it is meant that the OPTR 30 is oriented such that the firststage regenerator 120 and the second stage regenerator 220 are orientedvertically or substantially vertically (relative to the gravity vector),such that the first and second stage cold heat exchangers 192 and 292are located at or adjacent the bottom ends of the respectiveregenerators, opposite the first and second stage hot heat exchangerslocated at or adjacent the top ends.

The construction of the OPTR 30 is best understood from a description ofthe flow path of the working fluid which is an oscillatory gas(preferably helium) therethrough, beginning from an oscillatory gaspressure power source or gas compressor 105, shown schematically in thefigures. As used herein, an oscillatory gas pressure power source is adevice or machine that delivers or provides positive gas pressure incyclic or recurring surges in a working fluid, preferably ofsubstantially equal pressure and volume (mass) of gas per surge(referred to herein as oscillatory gas), measurable in surges or cyclesper second, or Hertz (Hz). While helium is preferred for the workingfluid, and the remaining description is provided for the case where theworking fluid is helium, it will be understood that another suitableworking fluid can be used in the OPTR 30.

Preferably, the oscillatory power source is a gas compressor 105,preferably an electric gas compressor, most preferably an electricflexure bearing linear drive compressor as will be further described.(The compressor 105 is omitted from FIGS. 2-3 to prevent obstruction ofdetails that otherwise would be masked by its presence in thesedrawings).

First, it should be noted that the ‘flow’ of oscillatory gas (preferablyhelium) refers to the propagation of the oscillation generated in theworking fluid (oscillatory gas) by the gas compressor 105, and conveyedto the OPTR 30 via transfer tube 101. Preferably, there is zero ornegligible (or substantially negligible) bulk mass flow of the workingfluid through the OPTR 30. In other words, individual helium atoms orquanta (assuming helium is the working fluid) oscillate betweengenerally fixed points within the OPTR 30, preferably with zero ornegligible net bulk flow. Without wishing to be bound to a particulartheory, it is believed that the oscillation of upstream (more adjacentto the gas compressor 105) helium atoms is transferred to downstream(more distal from the gas compressor 105) helium atoms by a pressureeffect; i.e. upstream helium atoms intermittently impact (at theoscillation frequency) helium atoms immediately adjacent and downstreamof the upstream atoms, thereby causing the downstream helium atoms tooscillate in phase with the upstream atoms and so on. The sum of thesepressure effects throughout the oscillatory helium flow path results inan overall pressure wave oscillation in the oscillatory helium withinthe OPTR 30 that is generated by the periodic pressure surges suppliedfrom the gas compressor 105. With the above in mind, it is alsounderstood and expected that the oscillating pressure wave may generatesome bulk mass flow of oscillatory helium through the OPTR 30. It is notexpected or intended that the absolute or bulk mass flow rate ofoscillatory helium through the OPTR 30 must be zero; only that such flowrate is preferably zero or negligible.

Oscillation of the working fluid (preferably helium) is generated by thegas compressor 105. The gas compressor 105 preferably is an electricflexure bearing linear drive compressor, which is preferred for a numberof reasons. First, it is electrically powered and electricity is readilyavailable in a home, business, or on the vehicle to provide the energyneeded to have a zero boil-off or no-vent storage system. The desired(ideal) operating frequency is 30 Hz, although a higher frequencybetween 30 and 60 Hz may be more desirable based on the heat absorptivematerials used in the regenerators 120 and 220 (described below). It isnot desirable to operate at less than 30 Hz because the compressor sizewill increase. The compressor operating frequency can be changed orregulated as a function of compressor input power should it be desirableto vary the frequency; e.g. in order to get higher operating frequenciesif desirable in the 30-60 Hz range. The inventors herein have used alinear flexure bearing compressor at an operating frequency variedgenerally between 28 and 32 Hz. Flexure bearing compressors generallyexhibit greater reliability and longevity, for example compared torotary valve compressors (such as used by Wang et al., cited above) andother conventional gas compressors. Flexure bearing compressors havebeen shown to operate for 5 to 10 years with no failures.

Oscillatory helium enters the first stage 100 of the OPTR 30 through thefirst stage aftercooler 110. The aftercooler 110 absorbs a substantialportion of the heat of compression and dampens temperature oscillationin the oscillatory helium flow prior to entering the first stageregenerator 120. The first stage regenerator 120 has an exterior shellor housing 121 enclosing a highly porous heat absorptive material 122.Most preferably, housing 121 is made from stainless steel, and isinsulated such that the regenerator 120 operates substantiallyadiabatically, or at least as adiabatically as possible. The heatabsorptive material 122 has high heat capacity and preferably low tomoderate thermal conductivity (if conductivity is too high,inefficiencies will occur due to heat transfer from the housing 121).Preferably, the thermal conductivity of heat absorptive material 122 isnot more than 28, preferably not more than 24, preferably not more than20, W/m-K at 60-100K, preferably 70-90K, preferably about 80K.Preferably, the heat absorptive material 122 in the first stageregenerator 120 has substantial heat capacity at a temperature of60-100K, preferably 70-90K, preferably about 80K. The heat absorptivematerial 122 in the first stage regenerator 120 preferably has avolumetric heat capacity of at least 1 J/cm³K, preferably 1.3 J/cm³K,preferably 1.8 J/cm³K, preferably 2.0 J/cm³K, preferably 2.2 J/cm³K, at60-100K, preferably 70-90K, preferably about 80K. Also, the heatabsorptive material 122 of the first stage regenerator 120 preferablyhas a porosity of at least 0.55, preferably 0.6, preferably 0.63,preferably 0.66 preferably 0.67, preferably 0.68. Preferably, the heatabsorptive material 122 is a plurality of layers of stainless steelscreen or mesh stacked axially or transversely within the housing 121. Afine stainless steel mesh is preferred, preferably having a mesh size of60-800, preferably 100-700, preferably 200-600, preferably 300-500,preferably 400, mesh. The mesh size is small enough to ensure maximumsurface area of contact, and therefore efficient heat transfer, betweenthe mesh and the oscillatory gas, but large enough not to significantlyimpede the oscillatory flow of helium therethrough. Preferably, thepressure drop across the heat absorptive material 122 in first stageregenerator 120 is not more than 1 psi, preferably not more than 0.4psi, preferably not more than 0.2 psi.

A first stage isothermal flow passage 130 connects the outlet of thefirst stage regenerator 120 to the inlet of the first stage pulse tube140 via the first stage cold heat exchanger 192. The first stage coldheat exchanger 192 has a refrigerant fluid flow passage coupled to andin fluid communication with a refrigerant line 3 that is connected inline with the second thermal jacket 44. The first stage cold heatexchanger 192 can have any suitable conventional configuration.Optionally, the first stage isothermal flow passage 130 and cold heatexchanger 192 can be combined or integrated into a single unit.

It is preferred that the working fluid-side of cold heat exchanger 192contains packed copper screen to increase convective heat transfer areafor the working fluid, effectively increasing heat transfer between theworking fluid and the refrigerant fluid in the heat exchanger 192. Thepreferred copper screen mesh size is 60-150, preferably 80-120,preferably 100, mesh.

In addition to the first stage cold heat exchanger 192, oscillatoryhelium flow also is delivered from the outlet of the first stageregenerator 120 to the inlet of the second stage regenerator 220. Inother words, oscillatory helium flow is split at the outlet of the firstregenerator 120, with part of the oscillatory helium flow being directedto the first stage cold heat exchanger 192 as just described, and theremainder being directed to the second stage regenerator 220. In apreferred embodiment, the first stage cold heat exchanger 192 isprovided with a single inlet and two outlets, one leading to the firststage pulse tube 140 and the other leading to the second stageregenerator 220. In this embodiment, the first stage cold heat exchanger192 serves two functions; in addition to being the first stage cold heatexchanger of the first stage 100, where the refrigerant fluid circulatedthrough the second thermal jacket 44 is refrigerated, it also serves asan aftercooler for the second stage 200 pulse tube refrigeration unit toregulate the initial helium temperature on entry into the second stageregenerator 220, and to dampen temperature oscillations on entrytherein.

Continuing with the first stage 100, oscillatory helium flow enters thefirst stage pulse tube 140 from the first stage cold heat exchanger 192.The first stage pulse tube 140 preferably is made from stainless steel.A first stage hot heat exchanger 150 is located immediately downstreamof the first stage pulse tube 140 which is preferably cooled by water orcoolant, e.g. using the vehicle's coolant system via conduit 115.Optionally, the hot heat exchanger 150 can be cooled via a forced aircooling system (not shown). Preferably, the first stage hot heatexchanger 150 is a shell-and-tube heat exchanger, less preferablyplate-and-fin, less preferably another suitable configuration, andpreferably it is made from copper. The tube side of hot heat exchanger150 is packed with copper screen having a mesh size of 60-150,preferably 80-120, preferably 100, mesh, to increase heat transferbetween the working fluid on the tube-side of hot heat exchanger 150 andthe tube wall which is cooled by water on the shell side. Preferably,the first stage hot heat exchanger 150 operates isothermally atsubstantially ambient temperature, preferably 300K. The first stage 100also has a first stage primary orifice 160, inertance tube 170 andreservoir volume 180, which are generally known components of an orificepulse tube refrigerator, and help improve and/or control refrigerationpower at the first stage cold heat exchanger 192. Preferably, inertancetube 170 and reservoir volume 180 are made from stainless steel. In thepreferred embodiment of FIGS. 1-3, the first stage reservoir volume 180is a toroid so that it fits conveniently within the overall structure ofthe system 10 as shown, yet still provides adequate reservoir volume. Inaddition, the inertance tube 170 can be several meters in length, andmay be coiled up or wound so that it fits within the space provided.

The first stage 100 also preferably has a secondary orifice 190connecting the first stage hot heat exchanger 150 to the transfer tube101. It has been found for an orifice pulse tube refrigerator that bytuning the secondary orifice 190, one can further improve coolingefficiency and reduce the operating temperature of the cold heatexchanger 192 of the first stage 100 refrigeration unit.

Turning now to the second stage 200 refrigeration unit, oscillatoryhelium flow is introduced into the second stage regenerator 220 from thefirst stage cold heat exchanger 192 as previously described. The secondstage regenerator 220 has similar construction to the first stageregenerator 120, preferably having a second stage regenerator housingmade from stainless steel. The heat absorptive material 222 in thesecond stage regenerator 220, however, preferably has adequate heatcapacity at or near the temperature of the cryogenic liquid hydrogenbeing stored in the storage vessel 20, e.g. 13-20K. Preferably, the heatabsorptive material 222 in the second stage regenerator 220 is orcomprises a rare earth metal or rare earth metal compound, preferably anerbium compound, more preferably an erbium-praseodymium compound,preferably in the form of spheres, less preferably some other discreteshape, less preferably in a matrix such as fixed particles on a poroussubstrate. When spheres are used, preferably the spheres have a meandiameter of 60 to 100 microns, more preferably 70 to 90 microns, mostpreferably 80 to 85 microns. Less preferably, the heat absorptivematerial 222 can be in any form that does not substantially raise thepressure drop across second stage regenerator 220, and still provideshigh surface area of contact between the heat absorptive material 222and the oscillatory helium gas. The heat absorptive material 222 in thesecond stage regenerator 220 preferably has a volumetric heat capacityof at least 0.23 J/cm³K, preferably 0.4 J/cm³K, preferably 0.6 J/cm³K,preferably 0.75 J/cm³K, most preferably 0.82 J/cm³K at 13-14K, and avolumetric heat capacity of at least 0.5 J/cm³K, preferably 0.6 J/cm³K,preferably 0.7 J/cm³K, most preferably 0.80 J/cm³K at 18-20K. Also, theheat absorptive material 222 of the second stage regenerator 220preferably has a porosity of 0.2-0.5, preferably 0.3-0.45, preferably0.36-0.4, preferably about 0.38.

Oscillatory helium flow exits the second stage regenerator 220 viasecond stage isothermal flow passage 230, and enters the second stagepulse tube 240 (preferably made from stainless steel) via the secondstage cold heat exchanger 292. Cold heat exchanger 292, preferably hassimilar construction, and is constructed of similar materials, as thefirst stage cold heat exchanger 192. The second stage cold heatexchanger 292 is where net refrigeration for the second stage 200occurs. Analogous to the first stage cold heat exchanger, the secondstage cold heat exchanger 292 also has a refrigerant fluid flow passagethat is coupled to and in fluid communication with a refrigerant line 4that is connected in line with the first thermal jacket 42. The secondstage cold heat exchanger 292 can have any suitable conventionalconfiguration. Optionally, the second stage isothermal flow passage 230and cold heat exchanger 292 can be combined or integrated into a singleunit.

Analogous to the first stage cold heat exchanger 192, it is preferredthat the working fluid-side of cold heat exchanger 292 contains packedcopper screen to increase convective heat transfer area for the workingfluid, effectively increasing heat transfer between the working fluidand the refrigerant fluid in the heat exchanger 292. The preferredcopper screen mesh size is 60-150, preferably 80-120, preferably 100,mesh. The oscillatory helium flow continues through the second stagepulse tube 240, and is delivered to the second stage hot heat exchanger250, second stage primary orifice 260, inertance tube 270 and reservoirvolume 280, similarly as for the first stage 100. The second stageinertance tube 270 and reservoir volume 280 are preferably made fromstainless steel, and in the embodiment of FIGS. 1-3, the reservoirvolume 280 also is provided as a toroid, similar to the first stagereservoir volume 180. The second stage hot heat exchanger 250 preferablyis of similar construction and materials as first-stage hot heatexchanger 150, it is operated isothermally at substantially ambienttemperature (preferably 300K), and is cooled by cooling water or coolantvia conduit 115 along with first stage hot heat exchanger 150. Inaddition, like the first stage 100, second stage 200 also preferably hasa secondary orifice 290 connecting the second stage hot heat exchanger250 to the transfer tube 101.

Optionally and preferably, the first and second stage hot heatexchangers 150 and 250 and the first stage aftercooler 110 can beprovided as an integrated structure as part of a common thermal block,or as thermally coupled blocks, all cooled by cooling water or coolantvia the conduit 115.

Preferably, all the operative cold components of the OPTR 30 (includingfirst and second stage regenerators 120,220, pulse tubes 140,240,isothermal flow passages 130,230 and cold heat exchangers 192,292) arecovered or wrapped with at least 0.1, preferably 0.3, preferably 0.5,preferably 0.8, preferably 0.9, preferably 1, inch of super insulationmaterial as described above, and are housed within the primary vacuumchamber 80 to minimize or prevent ambient heat transfer thereto.

In operation, the liquid hydrogen storage system 10 functions asfollows.

Initially, the OPTR 30 is charged with a working fluid, preferablyhelium gas, at 200-1000, preferably 300-900, preferably 400-700,preferably 430-600, preferably 450-550, preferably 480-530, preferably490-510, preferably about 500, psia. The gas compressor 105 providesoscillatory gas pressure to operate the OPTR 30. Oscillatory helium flowgenerated by the gas compressor 105 is delivered to the OPTR 30 throughtransfer tube 101.

It will be understood that helium oscillation within the OPTR 30 resultsin an oscillatory pressure ratio (P_(max)/P_(min)) between thecompressive and expansive phases of a given quantum of helium. Thispressure ratio varies with position in the helium flow path through theOPTR 30. The larger the pressure ratio the greater power generated. Thepreferred pressure ratio at the inlet to the first stage pulse tube 140is 1-1.3, preferably 1-1.25, preferably 1.1-1.23, preferably 1.15-1.22,preferably 1.2. The preferred pressure ratio upon exiting the gascompressor 20 is 1.2-1.4, preferably 1.25-1.35, preferably 1.26-1.34,preferably 1.28-1.32, preferably 1.3.

Beginning with the first stage 100, the first stage regenerator 120receives oscillatory helium flow from the transfer tube 101. As thehelium gas oscillates, it undergoes successive compression and expansioncycles, each quantum of helium gas experiencing a temperature increasewith compression and a temperature decrease with expansion. Within thefirst stage regenerator 120, the heat absorptive material 122 absorbsthe heat of compression from a quantum of helium gas during thecompression phase, and delivers that stored heat energy back to the gasduring the expansion phase. This net effect proceeds down the length ofthe regenerator 120 until at the first stage isothermal flow passage130, the temperature of the helium gas has been reduced to substantiallythe operating temperature of the first stage cold heat exchanger 192,preferably 60-100, preferably 70-90, preferably about 80, degreesKelvin. Thus, oscillatory helium delivered to the first stage cold heatexchanger 192 from the first stage regenerator 120 causes substantiallyno net heating effect (either heating or cooling) at the first stagecold heat exchanger 192. That is, the oscillating helium arrives at thefirst stage regenerator 120 already cooled to the steady state operatingtemperature of the regenerator 120.

The first stage cold heat exchanger 192 preferably is operatedisothermally at steady state, preferably at 40-120, preferably 50-110,preferably 60-100, preferably 70-90, preferably about 80, degreesKelvin. The refrigerant circulating through the cold heat exchanger 192(and the second thermal jacket 44) preferably is helium, though nitrogenalso is suitable at operating temperatures of about 80K. At the firststage cold heat exchanger 192, the oscillatory helium flow is split asdescribed above. With respect to the first stage pulse tube 140,oscillatory helium gas within the pulse tube 140 shuttles heat energyfrom the cold heat exchanger 192 against the temperature gradient inpulse tube 140 as known in the art, to be expelled via the first stagehot heat exchanger 150. In this manner, net refrigeration power isgenerated at the cold heat exchanger 192 effective to refrigerate therefrigerant fluid being circulated therethrough and through the secondthermal jacket 44 via pump 8. In this manner, the second thermal jacket44 is maintained at low temperature, preferably about 80K, viacirculation of the refrigerant through the jacket 44 via line 3 and pump8, and is effective to abate heat transfer from the ambient atmospheretoward the liquid storage vessel 20.

Oscillatory helium flow also is delivered to the second stageregenerator 220 from the first stage cold heat exchanger 192 asdescribed above. Analogous to the first stage regenerator 120, thesecond stage regenerator 220 lowers the helium temperature from that ofthe first stage cold heat exchanger 192 to substantially that of thesecond stage cold heat exchanger 292. It is important to minimize heattransfer to the second stage cold heat exchanger 292 from the firststage 100 refrigeration unit in order to maximize cooling efficiency atthe cold heat exchanger 292. Therefore, the heat absorptive material 222used in the second stage regenerator 220 is specially selected to ensuremaximum cooling of the oscillatory helium prior to entering the secondstage cold heat exchanger 292. As stated above, the heat absorptivematerial 222 in second stage regenerator 220 preferably is a rare earthmetal or metal compound.

Cold heat exchanger 292 preferably operates isothermally, preferably ata temperature of 13-20K. Preferably, the refrigerant fluid circulatingthrough the second stage cold heat exchanger 292 (and the first coolingjacket 42) is helium.

Oscillatory helium gas within the second stage pulse tube 240 shuttlesheat energy from the second stage cold heat exchanger 292, to beexpelled via the second stage hot heat exchanger 250 as known in theart. The second stage 200 (second stage pulse tube 240) therebygenerates net refrigeration power at the cold heat exchanger 292,similarly to the first stage 100 (and first stage pulse tube 140). Thenet refrigeration power at the cold heat exchanger 292 is effective torefrigerate the refrigerant fluid being circulated therethrough andthrough the first thermal jacket 42 via pump 9. In this manner, thefirst thermal jacket 42 is maintained at low temperature, preferablyabout 13-20K, via circulation of the refrigerant through the jacket 42via line 4 and pump 9, and it is effective to further abate heattransfer from the ambient atmosphere toward the liquid storage vessel20, and to maintain the vessel 20 in the range of 13-20K. The result isthat liquid hydrogen 5 within the vessel 20 is maintained below itssaturation or boiling point temperature, and vaporization and boil offare minimized or prevented. This reduces or eliminates the need to ventgaseous hydrogen to relieve hydrogen overpressure because none orsubstantially none is generated.

It should be noted there is no fluid communication between either thefirst or second thermal jackets 42 or 44 (or the associated refrigerantlines 4 or 3) and the working fluid pathway in the OPTR 30, even thoughhelium is the preferred working fluid in the OPTR and helium also can beand preferably is used as a refrigerant for one or both of the thermaljackets.

The pumps 8 and 9 that pump the refrigerant fluids through therespective second and first thermal jackets 44 and 42 preferably are lowpressure drop, low flow rate pumps as known in the art. Preferably, thepumps 8 and 9 have a pressure drop of less than 0.1 psi, less preferably0.5 psi, and are designed to be operated at the respective operatingtemperatures of the refrigerants (˜60-120K and ˜13-20K). The pump 9 usedto circulate the more highly refrigerated refrigerant fluid (T˜13-20K)can be actively cooled through heat exchange with the relatively hightemperature refrigerant fluid line 3 as illustrated in FIG. 1. Thisensures the least possible heat transfer to the low temperaturerefrigerant in the line 4 due to heat generation at the pump 9.

The gas compressor 105 used to drive the OPTR 30 can be powered from anyone of three power sources depending on the state of the vehicle:external, vehicle alternator/battery power, or hydrogen/air fuel cellpower. An external source of power is preferred when the vehicle isparked or not in use. It is contemplated that parking spaces forhydrogen-powered automobiles could be equipped with power couplings orpower sockets at relatively little expense; the driver simply would“plug in” his automobile once parked in order to continue providingpower to the gas compressor 105. However, it is noted that the storagevessel 20 is very well insulated and it is anticipated that the systemcould sit dormant for a reasonable period of time, such as 1-2 days,before it would be necessary to engage the OPTR 30 to cool the vessel 20to relieve hydrogen overpressure. Thus, if a vehicle will be parked fora relatively short time, such as less than 2 days, it probably would beunnecessary to connect the OPTR to power during that time. When thevehicle is running or in use, then the power to drive the compressor 105is supplied from the vehicle's own electrical system or alternator torun the OPTR 30 and generate refrigeration power.

In the case where the vehicle is to remain off for long periods of timeand no external power source is available, a hydrogen/air fuel cellpower system can be provided and employed as follows. With no power todrive the gas compressor 105, eventually liquid hydrogen within thevessel 20 will vaporize and require venting. The headspace of the innervessel 20 is equipped with a hydrogen vent 107 that is designed torelease hydrogen overpressure at a certain cracking pressure of anoverpressure valve (not shown). For example, the hydrogen vent 107 canbe or utilize a resealable pressure relief valve that cracks at acertain cracking pressure, allowing hydrogen overpressure to escape. Thevalve reseals once the overpressure has subsided below the valvecracking pressure. Resealable pressure relief valves are known orconventional in the art, and any such valve can be used so long as it iscompatible with hydrogen and with the temperatures it will experience(e.g. 20K).

The vented hydrogen gas is delivered to a hydrogen/air fuel cell thatconverts the vented hydrogen into electricity. Hydrogen/air fuel cellsare well known in the art; the products of such a fuel cell are waterand electricity. In this embodiment, the water is discarded and theelectricity can be stored in onboard batteries or used directly to drivethe gas compressor 105. As hydrogen is vented, the electricity generatedcharges onboard batteries which power the gas compressor 105 to recoolthe liquid hydrogen remaining in the vessel 20 below its saturationtemperature, causing vaporization to cease and resulting in a loss ofhydrogen overpressure and the closure of the hydrogen vent 107. Theoverall result is that vented hydrogen is converted into electricity ina closed system so there is no net hydrogen venting to the atmospherefrom the vehicle. The generated electricity is used to charge onboardbatteries used to power the compressor 105 to recool the liquid hydrogenand thereby stop further venting. It will be understood that for a longperiod of nonuse of the vehicle, eventually all of the liquid hydrogenwould be depleted. But, by the present invention the depletion rate isgreatly reduced compared to straight hydrogen venting, resulting insignificant cost and energy savings. In addition, the invention alsoprevents hydrogen venting to the atmosphere, eliminating a significanthazard heretofore associated with hydrogen-powered automobiles or othervehicles that has largely inhibited further development by automobilemanufacturers.

Liquid hydrogen 5 is delivered into the storage vessel 20 through a fillline 108 extending through the housing 50, super insulation 60 and thefirst and second thermal jackets 42 and 44, into the vessel 20, andprovided centrally within the vent line 107. Cold gaseous hydrogen thatvaporizes during the filling process, which is not recondensed on thecold vessel 20 wall, vents through the vent line 107 and keep the liquidfill line 108 cold, thus reducing further hydrogen vaporization.

It has been estimated experimentally that for a toroidal vessel 20insulated as described in the disclosed construction and sized to hold10 kg of liquid hydrogen, the amount of ambient heat transfer into thevessel 20, at an ambient temperature of about 300K, is about 1 watt.Based on this determination, about 1 watt of refrigeration power at thesecond stage cold heat exchanger 292, operating at 13K, and about 4-5watts of refrigeration power at the first stage cold heat exchanger 192,operating at 80K, is sufficient to counteract ambient heat transfer intothe vessel 20 given the construction (first and second thermal jackets42 and 44, super insulation 60 and primary vacuum chamber 80) describedherein, and further to cool liquid hydrogen in the vessel 20 below 20K.It is important to note that 4-6 watts of refrigeration power issufficient to sustain the liquid hydrogen without boil-off because thehydrogen is delivered to the vessel 20 as a cryogenic liquid, already ator below 20K. Therefore, refrigeration power is necessary only tocounteract the rate of ambient heat transfer into the vessel 20, and notto extract latent heat of vaporization to condense gaseous hydrogen. TheOPTR 30 generally is not used to condense gaseous hydrogen to providecryogenic liquid; though it could be used for this purpose, but wouldrequire a substantial amount of time at 4-6 watts of refrigerationpower, assuming room temperature hydrogen gas as the starting fluid.

In the preferred embodiment described above, the OPTR 30 can be scaledsuch that the first stage cold heat exchanger 192 operates at about 80Kand is effective to refrigerate the refrigerant circulating through thesecond thermal jacket 44 (i.e. to remove thermal energy therefrom) at arate of about 5 watts, and the second stage cold heat exchanger 292operates at about 13K and is effective to refrigerate the refrigerantcirculating through the first thermal jacket 42 at a rate of about 1watt. Thirteen degrees Kelvin is the triple point of hydrogen, andrepresents the densest possible condition for liquid hydrogen. It isimportant to note that operating at 13K and 1 watt, the second stagecold heat exchanger 292 is designed to counteract or balance against therate of ambient heat transfer into the inner vessel 20 in order tomaintain the liquid hydrogen at or near its triple point; it will beless effective at removing sensible heat to supercool saturated liquidhydrogen at 20K down to its triple point temperature of 13K. The secondstage cold heat exchanger 292 will operate at somewhat higher power(e.g. 2 or 3 watts or more) at higher temperatures (up to 20K) withoutresealing the OPTR, effective to remove more thermal energy from thevessel 20 and the liquid hydrogen within.

However, the OPTR 30 can be scaled to deliver a higher degree ofrefrigeration power at the second stage cold heat exchanger 292. Forexample, the OPTR 30 can be scaled to provide, 1, 2, 3, 4, 5, 6, 7, 8,9, 10, etc., watts of refrigeration power at the second stage cold heatexchanger 292. The preferred method for scaling the OPTR 30 is to adjustthe diameter of the oscillatory helium flow path for each componentwithin the OPTR 30 while keeping the length of each componentessentially constant. Increased power for refrigeration requiresadditional mass flow rate. It will be understood that increasing thediameter (cross-sectional area) of the helium flow path through eachcomponent of the OPTR 30 to accommodate increased mass (and thereforevolumetric) flow results in a constant oscillatory helium velocityindependent of refrigeration power. It is preferred to maintain aconstant oscillatory helium velocity when scaling the invented liquidhydrogen storage system 10. The above scaling method is particularlypreferred for non-hollow tube components such as the regenerators120,220.

In addition to the system as described above for storing cryogenicliquid hydrogen 5 in the vessel 20, the system can be optimized forstoring low temperature, high pressure gaseous hydrogen as well. In thisembodiment, the vessel 20 must be constructed of suitable material andsuitable wall thickness to withstand high pressure gas, e.g. up to 9000,10,000 or 12,000 psia, or higher. In order to store a comparable mass ofhydrogen in the gaseous state (relative to liquid hydrogen), it will benecessary to compress the hydrogen to at least about 7500 psia. This canbe achieved by maintaining the hydrogen gas at low temperature, e.g. inthe range of 70-100, preferably about 80, degrees Kelvin. If such highpressure, low temperature hydrogen gas is to be stored in the vessel 20,then only the first stage 100 of the OPTR 30 (and only one thermaljacket 44) described above is required to supply the necessary coolingduty at about 80K. That is, instead of the two-stage OPTR describedabove, only a single stage operating at a steady state temperature (coldheat exchanger 192) of about 70-100, preferably 80, degrees Kelvin needbe used. The advantages of this system over the low pressure liquidhydrogen system 10 described above include: less refrigeration powerrequired to sustain the hydrogen, nitrogen gas can be used as therefrigerant fluid instead of helium which is necessary for lowertemperatures such as 20K, and it has a decreased parts count, which maylead to lower total capital cost. Disadvantages of this high pressure,low temperature gaseous system are that the hydrogen must be maintainedat a pressure of at least 7500 psia at 80K to achieve comparable densityto liquid hydrogen, and the system may be heavier than the low pressureliquid system due to the thickness of the high pressure storage vesselwall. In addition, the gaseous storage system inherently is moredangerous than the liquid system because of the high energy (highpressure) state of the hydrogen.

Referring now to FIG. 5, an alternate embodiment of the invention isshown. In this embodiment, the liquid hydrogen storage vessel 320 isprovided generally as a rectilinear vessel having a sump region 321 ator adjacent the bottom of the vessel 320.

The storage vessel 320 is fixed within an outer housing 350 via lowconductivity spacer supports 362 provided between the inner vessel 320and the housing 350. The spacer supports 362 preferably are made fromsimilar materials as described above for the spacer supports 62 in FIGS.1-3. An intermediate or interpositional space 348 is provided anddefined between the housing 350 and the vessel 320. The interpositional348 space preferably is maintained under vacuum to provide a vacuumchamber as described above. In addition, the interpositional space 348is provided with super insulation 360, also as described above.

In this embodiment, both first 100 and second 200 stages of the OPTR 30are enclosed or partially enclosed within a radiation shield 191, whichis thermally coupled to and cooled by the first stage cold heatexchanger 192. Preferably, at least the second stage regenerator 220 anda portion of the second stage pulse tube 240 are located within theradiation shield 191. Preferably, the radiation shield 191 is made fromthin-walled aluminum, and is cooled to or maintained at a temperature ofabout 80K by the first stage cold heat exchanger 192. The 80K aluminumradiation shield presents an additional barrier against thermalradiation from the ambient atmosphere into the OPTR components, and alsotoward the base of the storage vessel 320 where the liquid hydrogen hasthe greatest surface contact due to gravity. Preferably, the radiationshield 191 encloses at least the sump region 321 of the vessel 320.

In this embodiment, the second stage cold heat exchanger is thermallycoupled to a heat transfer body such as a fin or fin structure 291projecting from the inner wall of the storage vessel 320, directly intoliquid hydrogen in the sump region 321. The fin structure 291 cancomprise one or a plurality of extending heat transfer fins as is knownin the art. In the second stage cold heat exchanger 292 heat energy isremoved from the liquid hydrogen directly via fin structure 291 withinthe sump region 321, instead of using a refrigerant fluid, to maintainthe liquid hydrogen below its saturation temperature. The second stagecold heat exchanger 292 extracts thermal energy from the fin structure291 to which it is thermally coupled, thereby cooling the cryogenicliquid hydrogen within the storage vessel 320. Consequently, there is noor substantially no boil-off of liquid hydrogen, and therefore no needto vent hydrogen overpressure.

The sump region 321 acts as a reservoir for cooled liquid hydrogen thathas been cooled by the fin structure 291. A fill/drain pipe 318 isconnected to a pump 314 and provides fluid communication between thepump 314 and a fill/drain port located at the exterior of the housing350. Liquid hydrogen fuel can be added to or extracted from the storagevessel 320 through the fill/drain pipe 318 by operation of the pump 314.The fill/drain pipe 318 is made from conventional materials capable ofwithstanding the temperature gradient it will experience (i.e. ambienttemperature outside the outer housing 350 down to cryogenic liquidhydrogen temperatures within the vessel 320 (13-20K). The fill/drainpipe 318 can be used to fill the vessel 320 with liquid hydrogen (asduring refueling) and also to supply hydrogen fuel to an engine or to afuel cell in a vehicle (not shown). Providing only a single fill/drainpathway eliminates a potential conductive heat transfer pathway from theambient environment into the vessel 320 by eliminating a second fill ordrain pipe. A suitable T-valve or other conventional valve or manifoldstructure or assembly can be used to permit liquid hydrogen deliveryinto the vessel 320 for refueling, as well as hydrogen fuel delivery toan automobile engine (or fuel cell) during operation.

A hydrogen delivery manifold can be equipped with appropriate meteringequipment for metering the amount of liquid hydrogen withdrawn from thestorage vessel 320 and delivered to an engine's combustion chamber or toa hydrogen powered fuel cell, e.g. in an automobile.

The liquid level (of hydrogen) in the vessel 320 preferably is measuredusing a flexible temperature and liquid level sensing probe 370 similarto that described above.

In the most preferred embodiment liquid hydrogen is maintained at ornear its triple point of about 13K, the densest possible condition forliquid hydrogen. This results in approximately 7 percent greaterhydrogen mass for a given storage volume compared to saturated liquidhydrogen at 20K, which is what would be present in a conventional ventedliquid hydrogen tank with no refrigeration. Benefits include reducedvessel size and consequent reduced vehicle mass for the same hydrogenstorage capacity.

Another principal advantage of a liquid hydrogen storage system 10according to the invention is that it eliminates the need for ventinghydrogen from the storage vessel 20,320 so long as a power source isavailable to operate the oscillatory power source. In addition, when ahydrogen/air fuel cell system is included as described above,atmospheric hydrogen venting is completely eliminated even if thevehicle is off or immobile for long periods. The substantial reductionor elimination of hydrogen venting is a necessity for the world tooperate in a hydrogen economy as opposed to an oil economy. It would becost prohibitive to provide venting and burn-off facilities at everylocation a vehicle will be parked for long periods. The elimination ofhydrogen venting provides for significantly safer operation ofhydrogen-powered automobiles and other vehicles.

Still another advantage is that the invented system 10 is effective tomaintain liquid hydrogen at or below the boiling point without venting,yet contains substantially no moving parts. The result is a system thatis reliable, simple to operate, and easily maintained. The inventionalso is inherently stable which increases reliability.

Although the hereinabove described embodiments of the inventionconstitute the preferred embodiments, it should be understood thatmodifications can be made thereto without departing from the spirit andthe scope of the invention as set forth in the appended claims.

1. A hydrogen storage and delivery system comprising a liquid hydrogenstorage vessel, an orifice pulse tube refrigerator, and a cooling systemcoupled to the orifice pulse tube refrigerator, said cooling systembeing adapted to counteract or abate heat transfer to the storage vesselfrom the ambient environment, said vessel being adapted to delivertherefrom a metered quantity of hydrogen on demand for use as a fuel,wherein no cold heat exchanger of said orifice pulse tube refrigeratorpenetrates the liquid hydrogen storage vessel.
 2. The system accordingto claim 1, said storage vessel being in the shape of a hollow toroidhaving an interior surface that defines a hydrogen storage volume of thestorage vessel.
 3. The system according to claim 2, said orifice pulsetube refrigerator extending in a void space that is defined by saidtoroidal storage vessel and is located at the geometric center thereof.4. The system according to claim 1, said cooling system comprising afirst thermal jacket exterior to and substantially enclosing saidstorage vessel, and a second thermal jacket exterior to andsubstantially enclosing said first thermal jacket.
 5. The systemaccording to claim 4, said orifice pulse tube refrigerator comprising afirst stage orifice pulse tube refrigeration unit and a second stageorifice pulse tube refrigeration unit that operates at a lowertemperature than the first stage refrigeration unit, said first stagerefrigeration unit being thermally coupled to said second thermaljacket, and said second stage refrigeration unit being thermally coupledto said first thermal jacket.
 6. The system according to claim 5, saidfirst stage refrigeration unit comprising a first stage cold heatexchanger having a first refrigerant fluid flow passage that is coupledto and in fluid communication with said second thermal jacket, saidsecond stage refrigeration unit comprising a second stage cold heatexchanger having a second refrigerant fluid flow passage that is coupledto and in fluid communication with said first thermal jacket, wherein afirst refrigerant fluid, refrigerated at said first stage cold heatexchanger to a first temperature, is circulated through said secondthermal jacket during operation of said system, and wherein a secondrefrigerant fluid, refrigerated at said second stage cold heat exchangerto a second temperature, is circulated through said first thermal jacketduring operation of said system.
 7. The system according to claim 1,said cooling system comprising a heat transfer body projecting directlyinto a hydrogen storage volume of said storage vessel, said heattransfer body being thermally coupled to said orifice pulse tuberefrigerator.
 8. The system according to claim 1, further comprising anoscillatory gas pressure power source coupled to said orifice pulse tuberefrigerator via a transfer tube, said orifice pulse tube refrigeratorcomprising a first stage orifice pulse tube refrigeration unit and asecond stage orifice pulse tube refrigeration unit, each of the firstand second stage refrigeration units comprising a respectiveregenerator, cold heat exchanger, pulse tube, hot heat exchanger,primary orifice, inertance tube, and reservoir volume, each of the firstand second stage refrigeration units further comprising a secondaryorifice connecting the respective hot heat exchanger to the transfertube.
 9. The system according to claim 2, said cooling system comprisinga first thermal jacket in the shape of a toroid located concentricallyadjacent and substantially enclosing the liquid hydrogen storage vessel.10. The system according to claim 9, said first thermal jacketcomprising a length of tubing coiled in the shape of a toroid around thestorage vessel and adapted to accommodate a flow of a first refrigerantfluid therethrough.
 11. A system according to claim 9, said coolingsystem further comprising a second thermal jacket in the shape of atoroid located concentrically adjacent and substantially enclosing saidfirst thermal jacket.
 12. A system according to claim 11, said secondthermal jacket comprising a length of tubing coiled in the shape of atoroid and adapted to accommodate a flow of a second refrigerant fluidtherethrough.
 13. The system according to claim 1, further comprising anouter housing defining a primary vacuum chamber therein, said liquidhydrogen storage vessel and said cooling system being disposed withinsaid primary vacuum chamber.
 14. The system according to claim 13,wherein operative cold components of said orifice pulse tuberefrigeration unit are disposed within said primary vacuum chamber. 15.A system according to claim 13, said housing further defining asecondary chamber, separate and apart from said primary vacuum chamber,said system further comprising relatively high temperature hydrogenconditioning equipment disposed within said secondary chamber.
 16. Asystem according to claim 15, said hydrogen conditioning equipmentcomprising a vaporizer coupled to said hydrogen storage vessel via adelivery pipe and adapted to receive liquid hydrogen therefrom, and apreheater coupled to said vaporizer and adapted to receive vaporizedhydrogen therefrom, said preheater being further adapted to heathydrogen gas vaporized in the vaporizer to a suitable temperature fordelivery to a hydrogen-powered internal combustion engine or to ahydrogen-powered fuel cell.
 17. A system according to claim 1, saidorifice pulse tube refrigerator comprising a first stage orifice pulsetube refrigeration unit and a second stage orifice pulse tuberefrigeration unit that operates at a lower temperature than the firststage refrigeration unit, each of the first and second stagerefrigeration units comprising a respective regenerator, cold heatexchanger, pulse tube and hot heat exchanger, said first stageregenerator having a first heat absorptive material therein, said firstheat absorptive material having a thermal conductivity not more than 28W/m-K at 60-100K, a volumetric heat capacity of at least 1 J/cm³K at60-100K, and a porosity of at least 0.55.
 18. A system according toclaim 1, said orifice pulse tube refrigerator comprising a first stageorifice pulse tube refrigeration unit and a second stage orifice pulsetube refrigeration unit that operates at a lower temperature than thefirst stage refrigeration unit, each of the first and second stagerefrigeration units comprising a respective regenerator, cold heatexchanger, pulse tube and hot heat exchanger, said second stageregenerator having a second heat absorptive material therein, saidsecond heat absorptive material having a volumetric heat capacity of atleast 0.23 J/cm³K at 13-14K, a volumetric heat capacity of at least 0.5J/cm³K at 18-20K, and a porosity of 0.2-0.5.
 19. A system according toclaim 18, said second heat absorptive material being provided as a rareearth metal or rare earth metal compound.
 20. A system according toclaim 18, said second heat absorptive material being selected from thegroup consisting of erbium compounds.
 21. A system according to claim18, said second heat absorptive material being selected from the groupconsisting of erbium-praseodymium compounds.
 22. A system according toclaim 8, said oscillatory gas pressure power source being a flexurebearing linear drive compressor.
 23. An automobile comprising ahydrogen-powered internal combustion engine and/or a hydrogen-poweredfuel cell, and a hydrogen storage and delivery system according toclaim
 1. 24. A hydrogen storage and delivery system comprising atoroidal liquid hydrogen storage vessel and an orifice pulse tuberefrigerator, said toroidal storage vessel having an interior surfacedefining a liquid hydrogen storage volume, said storage vessel furtherdefining a void space located at the geometric center of the storagevessel, said orifice pulse tube refrigerator extending within said voidspace at the geometric center of the storage vessel.
 25. The systemaccording to claim 24, said orifice pulse tube refrigerator comprising afirst stage pulse tube refrigeration unit and a second stage pulse tuberefrigeration unit, each of the first and second stage refrigerationunits comprising a respective regenerator, cold heat exchanger, pulsetube and hot heat exchanger, wherein net refrigeration power for each ofthe first and second stage refrigeration units is generated at therespective first and second stage cold heat exchangers, and wherein thesecond stage cold heat exchanger operates at a lower temperature thanthe first stage cold heat exchanger.
 26. The system according to claim24, further comprising an oscillatory gas pressure power source coupledto said orifice pulse tube refrigerator and adapted to provide periodicpressure surges in a working fluid to drive the orifice pulse tuberefrigerator to thereby generate refrigeration power at said first andsecond stage cold heat exchangers.
 27. The system according to claim 1,further comprising a liquid level sensing probe disposed within saidstorage vessel, said liquid level sensing probe comprising a pluralityof adhered flexible dielectric strips and a series of temperaturesensing units disposed at spaced intervals along the length of theprobe, said probe remaining flexible at a temperature of 80K.
 28. Thesystem according to claim 1, further comprising hydrogen conditioningequipment adapted to condition hydrogen drawn from said storage vesselto provide conditioned hydrogen in a suitable state for delivery to anengine or fuel cell that consumes said conditioned hydrogen as fuel.